The present invention relates to apparatus and methods of capacitance measurements, in particular capacitive sensors and capacitance of cables connected to configurable electronic controllers useful in automotive and industrial automation.
Automotive and industrial electronic control systems use capacitive sensors for measurement of e.g., pressure, humidity and in-position sensing, liquid level, touch switches, and other control applications. For this purpose an electronic controller is preferably equipped with a capacitance-to-digital conversion module such as, for example, type AD7745 by Analog Devices. This circuitry is intended for capacitance measurements only and is not suitable for acquisition, by the same input, of another sensor type, for example voltage or current sensors.
A more flexible solution is the Sensor Signal Processor Chip type SSP1492 by Sensor Platforms Inc. This signal processor may be configured to accept capacitive, inductive or resistive sensor types, but each configuration is determined by external components, which cannot be changed in real time operation. In other words, in order to configure the signal acquisition of another sensor type the printed board components must be changed. This is quite problematic from the logistics and economical point of view.
The configurable electronic controller described in WO 2005/029207 (to V. Burkatovsky) is configured, by means of software commands, to perform measurements, on the same input pins, of different input signal parameters such as voltage, current and resistance as well as accept digital On-Off detectors. Another related invention described in WO 2006/008732 (V. Burkatovsky) describes means and method of input signal interconnect detection for such configurable electronic controllers.
It is one object of the present invention to provide a capacitance measurement technique for computerized control, and particularly controls based on configurable electronic controller architecture of the type described in the above-mentioned WO 2005/029207.
The field of electrical cable diagnostics is an important section in industrial and automotive control technology. Cables which are usually used, in such applications, have consistent geometry and may vary in length from dozens of centimeters to dozens of meters. Disconnections or damage resulting in cable breaks are considered a major failure in machine control, and impose on service personnel the use of special purpose tools to localize the failure for subsequent repair.
Diagnostics of breaks in cables is mentioned, for example, in the Infineon Current Sense TLE4990 data sheet (Clamping option). Tools for cable testing are described in, for example, in U.S. Pat. No. 6,868,357, utilizing the principles of Frequency Domain Reflectometry (FDR). Other devices as described in, for example, U.S. Pat. No. 6,646,454, U.S. Pat. No. 5,339,022, U.S. Pat. No. 5,493,650, and U.S. Pat. No. 6,181,140 determine cable length by measuring frequency/capacitance characteristics of the tested cable.
U.S. Pat. No. 6,459,271 describe a device for locating faults in a cable by applying a DC voltage step function to one end of the conductor, measuring the DC current into the conductor at the one end over a sampling period, integrating the DC current measured over the sampling period and computing the distance between the one end of the conductor to the open circuit fault by the integrated DC current and the known capacitance/unit length of the conductor.
These described devices are implemented as test and measurement tools with specific purposes of measuring the capacitance or cable length, as well as cable break detection and localization, and are not intended for machine control purposes.
It is another object of the present invention to provide a method for localizing breaks in wires and cables connected to electronic controllers, by capacitance measurement techniques based on configurable electronic controller architecture of the type described in above mentioned WO 2005/029207. In this method, the same controller will be able to accept signals of all kinds on its inputs, generate control signals on its outputs, and measure cable capacitance in order to detect and localize the cable breaks and perform harness diagnostics.